Wind turbines are normally placed far away from other tall structures and are therefore exposed to impact from lightning. Wind turbine blades are typically manufactured of a glass fibre laminate which can be seriously damaged by lightning impact. To prevent such damage the blades are provided with metallic lightning receptors which are mounted in the blade in such a way that the surface of a receptor is essentially in the plane of the outer skin of the blade. These receptors are then connected to ground through heavy gauge conductors.
The temperature of the air surrounding a lightning bolt can reach several thousand ° C. When lightning strikes a lightning receptor some of the energy of the air is transferred to the surface of the blade next to the receptor. This can lead to scorching of the paint and in some cases also of the underlying laminate. Thus, the integrity of the surface of the blade is compromised and the laminate is exposed to the atmosphere. The humidity can then penetrate the damaged parts of the laminate and lead to either a softening of the laminate or to spalling. The conventional way of reacting to the problem is to register the lightning impacts and then repair the damage that may have occurred.